Burner method and apparatus

ABSTRACT

A burner or torch system for mixing fuel with air and includes a fluid oscillator for forming a jet or sheet of fuel and oscillating the jet in ambient air downstream of the fluid oscillator. This mixes air with fuel and achieves a combustible mixture a distance spaced from any physical structure of the burner or torch whereby a flame front of burning combustible mixture has a shape and distance from the fluid oscillator which is determined by the sweep angle, wave pattern and frequency of the fluid oscillator. Various forms of fluidic oscillators are disclosed.

BACKGROUND AND BRIEF DESCRIPTION OF THE INVENTION

The present invention relates to burner method and apparatus whereinfuels such as gas must have a stoichiometric air/fuel mixture forpurposes of combustion to achieve the most efficient flamecharacteristics.

In conventional propane gas torches, for example, the burner nozzle hasa chamber for mixing stoichiometric ratio to achieve a blue flame whichhas a point of highest temperature to be the most efficient use of fuel.Heating of an object having a large surface area requires passing thetorch flame tip back and forth over the area or using a diffusing nozzleto heat it somewhat uniformly.

According to the present invention, a fluidic oscillator incorporated inthe burner nozzle sweeps the jet of fuel, which may be somewhatinternally mixed with air inside the mixing chamber but most or all ofthe mixing with air is achieved outside of and downstream of the nozzleand within a predetermined distance. The swept jet fuel mixes with airin the space between the outlet opening so that upon combustion itproduces a flame front having an area and thickness determined by thesweep angle and wave pattern of the fluidic oscillator and the rate ofmixing proportional to frequency of oscillation is self-regulating toachieve a proper fuel-air ratio needed for combustion. A wide variety offluidic oscillators are known and useful in practicing of the invention.

Advantages of the invention are that the shape of the hot flame front isexpanded and spaced from the physical burner nozzle to achieve a highheat transfer efficiency while at the same time, the physical nozzleremains cool and thus in some applications can be made of plastic.Moreover, by providing oscillators with different frequency ofoscillation, and wave patterns, the distance of the flame front and theshape thereof can be adjusted to accommodate different use services orapplications.

Almost any fluidic oscillator in which the fuel can be formed into anoscillatable or sweepable jet e.g., a jet that is oscillatable that issufficient to achieve proper mixing of fuel to be combustible apredetermined distance from the nozzle can be used. Such devices areshown in U.S. Pat. No. 4,052,002 for controlled fluid dispersaltechniques, Bray U.S. Pat. Nos. 4,463,904 and 4,645,126, Stouffer U.S.Pat. No. 4,508,267 and Stouffer and Bauer U.S. Pat. No. Re. 33,158 areuseful. In the preferred embodiment, it is desired to achieve as muchexternal mixing of the fuel with air as is possible to have as large adetached flame front as possible. In some cases however, fluidicoscillators having diverging outlets sweep the fuel jet back and forthand entrain some air into the nozzle and hence these are likewise usefulbut do not have as large a spacing between the flame front and thenozzle because there is less efficient external mixing of fuel with airto achieve the stoichiometric ratio.

DESCRIPTION OF THE DRAWINGS

The above and other objects, advantages and features of the inventionwill become more apparent when considered with the followingspecification and accompanying drawings wherein:

FIG. 1a is a diagrammatic perspective view of a conventional prior artpropane torch, FIG. 1b is an enlarged view of the nozzle, and FIG. 1c isa flame spreader,

FIG. 2 is a generalized diagrammatic illustration of a propane torch andnozzle incorporating the invention showing the sweeping jet and thedetachment of the flame front with the distance between the flame frontand the nozzle forming a mixing area for achieving the stoichiometricgas/air mixture for proper combustion,

FIGS. 3a, b, c, d, and e are diagrammatic illustrations of variousfluidic oscillators which are useful in practicing the invention,

FIGS. 4a-4f are diagrammatic illustrations of various prior art fluidicoscillator silhouettes useful in practicing the invention,

FIG. 5 is a diagrammatic illustration of a furnace burner wherein aplurality of fluidic burner nozzles are arrayed in one or more lines andcoupled to one or more fuel manifold,

FIGS. 6a and 6b are diagrammatic illustrations of stove top burners;wherein a plurality of fluidic burner nozzles are arrayed in apredetermined pattern such as a circle, or crossed and coupled to acommon fuel manifold, and

FIG. 7 is a diagrammatic illustration of a fluidic oscillation of thetype shown in Stouffer U.S. Pat. No. 4,151,955 for issuing a jet in theform of a sheet of fuel which is oscillated to achieve a combustibleair-fuel mixture.

DETAILED DESCRIPTION OF THE INVENTION

The conventional propane torch is illustrated in FIG. 1 being mounted ona FUEL tank 10 through a conventional threaded fitment 11 securing thetorch 12 to tank 10. It will be appreciated that flexible tubing,pressure gauges, regulators and like arrangements may be likewiseutilized. A valve 13 controls the flow of fuel (propane in thisembodiment) from propane tank 10 to the torch nozzle proper 14. Torchnozzle proper 14 is threadably secured to the threaded end 15 of pipe16. An aperture or orifice 17 (typically about 0.003" in diameter)issues a jet of propane fuel into a chamber 18 which is provided with aseries of openings 19 through Which air is entrained by the flow of jet18 into chamber C. By adjusting the valve 13, the proper air/fuel ratiois achieved so that a well defined blue flame 20 having a tip 21 with atrailing transparent blue flame portion 21T is achieved. The spacing ofthe flame front 20 from the nozzle end 22 is in most cases nonexistent.Thus, the nozzle 14 typically will heat up.

Most importantly however is that the flame front 20 is elongated into atip having a typical "flame" shape with which the hot spot is aroundapproximate the tip 21. A flame diffuser or spreader FS (FIG. 1c) can beattached to the end of the chamber C to broaden the flame. The deviceshown in FIG. 1 includes a conventional safety devices such as a flamearrester FA such that when the fuel pressure drops to such a low levelthat it is not able to project beyond the confines of the device, theflame does not spread back to ignite fuel in the tank.

There are numerous other prior art systems, in some of which air isentrained through an opening in pipe 16, for example, and premixed withair so that in the torch chamber C itself, less air is required to beentrained to achieve a proper fuel-air ratio to support combustion.

Referring now to FIG. 2, a fuel tank such as a propane tank 30 and valve31 has tube or pipe 32 (which is identical to tube or pipe 16 and alsomay include the conventional premix entrainment orifices and the like aswell as the safety devices described above) is fitted on its threadedend 33 with a fluidic oscillator nozzle 34 which produces a jet of fuelwhich is swept through an angle (α) in a mixing zone Z to support acombustion flame front FF which is spaced a distance D from the end 35of fluidic oscillator nozzle 34. This distance D and the shape of theflame front FF are significant improvements achieved by the presentinvention. Sweeping the jet stream of fuel through the angle (α) and ata predetermined rate (for example, about 1 to 3 kHz) results in anefficient mixing with air to achieve the proper fuel-air mixture at adistance D downstream of the nozzle so as that the nozzle itself willremain cool and the flame front FF can be shaped to be a broad hot flamefront. Thus, instead of having to oscillate the nozzle back and forth toheat-up a broad surface area, the nozzle is held stationary and theflame front is shaped to have a length L and the thickness T. Thus, incomparison to the flame front for the conventional torch, the presentinvention provides a broad area flame front which is significantlyspaced from the nozzle so that the nozzle remains essentially cool(radiant heat reflected from a heated object, of course can heat thenozzle) but is counteracted by cool, expanding fuel making the nozzlemore efficient (because inter alia the heat from the torch itself issupplied to the object rather than to heating-up the nozzle).

FIGS. 3a, 3b and 3c diagrammatically illustrate the sweeping output fromfluidic oscillators FO1, FO2 and FO3. In the oscillator FO1, the endFIG. 3a, the oscillator is designed to provide a sinusoidal sweep of thefuel, and if a stop motion strobe is projected on the output stream, thewaveform is essentially a sinusoidal shape. In the fluidic oscillator ofFIG. 3b, the fluidic oscillator FO2 has a triangular-shaped output andin FIG. 3c, fluidic oscillator FO3 has a traposoidal output. That is,there is a dwell resulting in more fuel being mixed with air at itsproper fuel-air ratio at the lateral ends of each sweep than in themiddle and resulting in a larger flame at those points.

When the fuel rate increases, the velocity of the sweep increasesproportionately but the wavelength remains constant and the mixing goeswith the frequency, double the frequency, double the mixing rate whichmeans that the proper fuel-air ratio is arrived at a distance closer tothe output edges 35. Thus, the shape of the flame front can be adjustedto accommodate targets and effect a higher heat transfer efficiencywhile maintaining a relatively cool nozzle. In some cases, the nozzlecan be made out of plastic, particularly in those situations whereradiant heat from the object being heated is low.

In FIGS. 4a, 4b, 4c, 4d, 4e and 4f, there are disclosed variousoscillator configurations useful in practicing the invention. In FIG.4a, the oscillator is of the type disclosed in U.S. Pat. No. Re. 33,158of Stouffer and Bauer entitled "FLUIDIC OSCILLATOR WITH RESONANTINERTANCE AND DYNAMIC COMPLIANCE CIRCUIT" and utilizes an inertance loopIL for oscillation. FIG. 4b discloses a fluidic oscillator of the typedisclosed in Stouffer U.S. Pat. No. 4,508,267 and depends on theformation and movement of vortices in the chamber to sustainoscillations. FIG. 4c discloses an oscillator of the type disclosed inBray U.S. Pat. No. 4,463,904. The oscillator shown in FIG. 4d is anisland oscillator of the type disclosed in Stouffer U.S. Pat. No.4,151,955. In FIG. 4e, the oscillator is of the type disclosed inStouffer and Bray U.S. Pat. No. 4,052,002. In each of these instances,the fluidic oscillator is of the type in which there is a single outletand the fuel exiting through the outlet of the device seals theoscillator chamber from ambient conditions. In the oscillator shown inFIG. 4e, the internal pressure of the device is greater than ambient sothat there is always an outflow of fluid.

In FIG. 4f, the oscillator is of the type disclosed in the Encyclopediaof Science and Technology (Von Nostrand). In this oscillator type, thereis entrainment of ambient air which serves to premix the fuel with airwith the fully combustible mixture being arrived through sweeping thefuel jet and at a distance spaced downstream of the edges of theoscillator. This is a less preferred embodiment of the invention becauseof its dependence on ambient air being drawn into the device itselfsomewhat in the fashion of the prior art nozzle discussed above.Moreover, because of this entrainment of ambient air, the flame front isspaced closer to the edge of the nozzle and the shape of the frame frontis less well controllable. These prior art references are incorporatedherein by reference and disclose the operating regimes thereof.

Operation of all fluidic oscillators is characterized by the cyclicaldeflection of the fuel jet without use of mechanical means of movingparts and consequently, the oscillators are not subject to wear and tearwhich adversely affects reliability and operation thereof. Moreover,since only the jet and not the entire orifice bearing body istranslated, less energy is required to achieve jet oscillation. SeeStouffer and Bray U.S. Pat. No. 4,052,002.

Various means can be utilized for varying the frequency of oscillation.For example, in the oscillator shown in FIG. 4a, by varying the lengthof the inertance IL, the frequency can be adjusted.

In the embodiment shown in FIG. 5, one or more arrays 60 ofdiagrammatically indicated fluidic oscillators 61-1, 61-2 . . . 61-N,62-1, 62-2 . . . 62-N, 60N-1, 60N-2, 60N-N on one or more gas fuelmanifolds 61, 62, 63 . . . 60N are supplied from a main supply 64through control valve CV. A pilot flame 96 is supplied with fuel bynozzle 67 which is valved at 69. Any of the types of fluidic oscillatornozzles disclosed herein may be used to oscillate the fuel stream inambient air to achieve a proper fuel air mixture for the most efficientcombustion. In FIG. 5, the broad shaped flame fronts FF61 are spacedfrom the oscillating nozzles a predetermined distance determined by thesweep angle; wave pattern and frequency of the fluidic oscillators 61-1,61-2 . . . 60N-1 . . . 60N-N.

If the oscillators are of the type which issues a sheet of fluid fuelwhich is oscillated as described above, then the broad flame front willhave a significantly larger area. The oscillator silhouette 70 shown inFIG. 7 is the type shown in the aforementioned Bray patents (but withouttaper) and is provided with a circular island 71 as shown in FIG. 20 ofStouffer U.S. Pat. No. 4,151,955. In this case the island 71 has beenpositioned out of the oscillator interaction region 73 to a generallycircular outlet region 72 and produces a swept sheet which is issued toambient.

Instead of being in linear array, the oscillator nozzles can be arrayedin a circle as shown in FIG. 6a or in transverse crossed array as shownin FIG. 6b, which also includes a plot flame 66. Moreover, while it ispreferred that the fluidic oscillators be of the same type, there may becases where the oscillators in one area issue a sweeping jet and inother areas a sweeping sheet is issued.

While there has been described and illustrated specific embodiments ofthe invention, it will be clear that various variations of the detailsof construction which are specifically illustrated and described may beresorted to without departing from the true spirit and scope of theinvention as defined in the appended claims.

What is claimed is:
 1. In a system for heating objects having a supplyof fluid fuel under pressure which is to be stoichiometrically mixed toachieve a combustible mixture, fluid fuel flow line connected to saidfluid fuel under pressure, a manual control valve in said fluid fuelflow line, a burner means for mixing air with said fluid fuel to achievesaid combustible mixture, characterized by said burner means includes afluidic oscillator for forming a jet of said fluid fuel and oscillatingsaid jet of fluid fuel in ambient air downstream of said fluidicoscillator to mix air with said fuel and achieve said combustiblemixture a distance spaced from any physical structure of said torchwhereby a flame front of burning combustible mixture has a broad shapeand is spaced a distance from said fluidic oscillator which isdetermined by the sweep angle, wave pattern and frequency of saidfluidic oscillator.
 2. A burner nozzle system for mixing fuel with airto attain a combustible fuel-air-mixture, comprising, a nozzle forcreating a jet of said fuel and means for oscillating said jet of fuelin the ambient air downstream of said means for oscillating to achievesaid combustible fuel-air-mixture at a distance spaced downstream fromsaid means for oscillating to maintain said means for oscillating cool.3. The burner system defined in claim 2 wherein said means foroscillating said jet of fuel is a no-moving part fluidic oscillator. 4.The burner system defined in claim 3 wherein said fluidic oscillator isof the type having an oscillation chamber with single outlet and fuelexiting said single outlet seals said oscillation chamber from ambientconditions.
 5. The burner system defined in claim 3 including means forvarying the frequency of oscillation of said fluidic oscillator.
 6. Theburner system defined in claim 3 wherein said fluidic oscillator is ofthe type which depends on the formation and movement of vortices of saidfuel to sustain oscillation.
 7. The burner system defined in claim 3wherein said fluidic oscillator is of the type which entrains ambientair to premix said fuel with entrained air.
 8. The burner system definedin any one of claims 2-7 wherein the rate of oscillation of said jet is1 to 3 kHz.
 9. The burner system defined in any one of claims 2-7wherein said means for oscillating is a fluidic oscillator and said jetis in the form of a sheet of fluid fuel.
 10. The method defined in claim9 including varying the rate of said oscillations.
 11. The methoddefined in claim 9 wherein said predetermined sweep rate is 1 to 3 kHz.12. The invention defined in claim 1 wherein there are a plurality ofsaid fluidic oscillators.
 13. The invention defined in claim 12 whereinsaid plurality of fluidic oscillators are arrayed in a predeterminedpattern.
 14. The invention defined in claim 2 wherein said means foroscillating includes a plurality of fluidic oscillators and means formounting said plurality of fluidic oscillators in a predeterminedpattern.
 15. A method of maintaining a burner nozzle cool duringoperation comprising creating a jet of fuel and oscillating said jet offuel in ambient air downstream of said burner nozzle through a sweepangle α at a predetermined sweep rate to mix the fuel with said ambientair and achieve a combustible mixture at a flame front a distance spaceddownstream from said torch nozzle to maintain said burner nozzle cool.16. In a system for heating objects having a supply of fluid fuel underpressure which is to be stoichiometrically mixed to achieve acombustible mixture, fluid fuel flow line connected to said fluid fuelunder pressure, control valve in said fluid fuel flow line, a burnermeans for mixing air with said fluid fuel to achieve said combustiblemixture, characterized by said burner means includes a fluidicoscillator for forming a sheet of said fluid fuel and oscillating saidsheet of fluid fuel in ambient air downstream of said fluidic oscillatorto mix air with said fuel and achieve said combustible mixture adistance spaced from any physical structure of said torch whereby aflame front of burning combustible mixture has a broad shape and isspaced a distance from said fluidic oscillator which is determined bythe sweep angle, wave pattern and frequency of said fluidic oscillator.17. The system defined in claim 16 including a plurality of said fluidicoscillators and means for mounting said plurality of fluidic oscillatorsin a patterned array.